亚热带森林土壤磷素形态构成及分异利用的生物多样性调控机理研究

Phosphorus (P) is an essential element required for plant growth. Efficient P management is mandatory because P often limits primary productivity in subtropical and tropical regions. The maintenance of soil P availability through species diverse forests might be an important ecosystem service as enhanced mineralization, accelerated nutrient cycle via higher litter production and decomposition, decreased nutrient loss in diverse mixed forests. Meanwhile, given the large range of biologically available soil P forms and compounds, and the variety of mechanisms by which plants can access P, we assume that co-existing plant species partition soil P to increase P use efficiency and reduce competition. . Here the aims of this study are to investigate the impacts of tree functional traits and tree species diversity on P forms formation on the stand level and neightbourhood species diversity combinations, and to assess possible niche separation among four native tree species, comprising two early successional species (Pinus massoniana and Choerospondias axillaris) and two late successional species (Lithocarpus glaber and Cyclobalanopsis glauca), for the utilization of different sources of soil P in a bioassay greenhouse experiment by using different substrates that contain some amount of total P per pot, but different forms of P derived from: a) topsoil with large proportion of organic P; b) subsoil with mostly inorganic P; c) mixed litter with solely organic P; d) mineral inorganic P fertilizer. Based on this we hypothesize: (i) soil P availability increases, while total P decreases with forest succession; (ii) soil P availability increases with tree species diversity; (iii) the overall efficiency of soil P utilization increases with tree species diversity and this complementary effect is more pronounced in substrates containing more diverse organic P sources (i.e. topsoil and litter substrates). In addition, the contributions of mycorrhizal symbiosis will be assessed. This project could provide valuable theoretical information for species diversity conservation and efficient P management in subtropical mixed forests.

磷（P）是植物生长发育不可缺少的营养元素，是热带和亚热带地区森林生长的限制性因素。营造混交林可能是提高土壤P素有效性，充分利用土壤潜在的P资源的重要举措。土壤磷素形态的多样性以及不同植物对土壤P限制吸收策略的多样性可能会产生共生植物P吸收的生态位分化，从而提高对土壤P的利用效率。本项目拟在林分尺度和邻域树种多样性水平研究凋落物分解和细根周转等生物过程对土壤P素形态构成及生物有效性的影响；通过不同P形态供应源的树种多样性盆栽实验，解析树种多样性对不同土壤P形态的互补利用机制，并验证以下三个科学假说：（1）土壤生物有效态P随着森林演替增加，但土壤总磷含量下降；（2）土壤有效态P随着树种多样性的增加而增加；（3）土壤P的总吸收效率随着生物多样性的增加而增加，而且这种互补效应因共生菌根的作用而增强，但随着土壤有机磷形态多样性的下降而减弱。项目的研究结果将为生物多样性保育和P的有效管理提供理论依据。

磷（P）是植物生长发育不可缺少的营养元素，是热带和亚热带地区森林生长的限制性因素。营造混交林可能是提高土壤P素有效性，充分利用土壤潜在的P资源的重要举措。本项目旨在探求土壤磷生物有效性及外源性影响机制及不同植物对土壤P限制吸收策略的多样性是否会产生共生植物P吸收的生态位分化，从而提高对土壤P的利用效率。. 本项目在湖南省大山冲森林公园内选择马尾松-石栎针阔混交林、南酸枣落叶阔叶林和石栎-青冈常绿阔叶林，分析植物磷与土壤磷库存关系；在林分尺度和邻域树种多样性水平研究凋落物分解和细根周转等生物过程对土壤P素形态构成及生物有效性的影响；通过不同P形态供应源的树种多样性盆栽实验，解析树种多样性对不同土壤P形态的互补利用机制。. 研究结果表明，随着森林演替磷贮量呈现先升高后降低的趋势，其中落叶阔叶林生态系统的磷贮量最大，达到1.66 Mg ha-1，而针阔混交林和常绿阔叶林的磷贮量差不多一样，分别为1.07 Mg ha-1和1.06 Mg ha-1，土壤磷库占生态系统总磷的95%以上，土壤生物有效磷的含量也是落叶阔叶林最高。在邻域树种多样性实验中，土壤总磷含量随树种多样性的增加大致表现为递减的趋势，土壤无机磷含量组分（NaHCO2-Pi和NaOH-Pi）所占比例随树种多样性的增加而减少，而土壤有机磷含量与地上年凋落物量和细根生物量呈显著正相关关系。不同形态磷供应比例的树种多样性盆栽实验结果表明，植物对土壤表层土即以有机磷和无机磷为共同磷源的土壤植物生长状况最好，但不同的树种多样性的植物生长量和磷吸收固持量并没有表现出显著的“超产”效应。本项目现有结果表明，不同生态系统磷贮量主要受土壤和植物的影响，土壤无机磷主要受植物吸收的影响，树种多样性可能会增加对土壤无机磷的吸收，而有机磷主要受植物地下和地下有机质输入的影响。此外，树种多样性对土壤磷的分异利用可能受植物大小和时间的影响。